w+*
.t+#
Antioxidants and the Autoxidation of Fats. 111’ Methods are described (1) for estimating the length of the induction period of lard and lard-cod liver oil mixtures by oxygen absorption, (2) for measuring the minute pressure changes occurring in a closed system during and immediately following the induction period, and (3) for determining the peroxide content of autoxidizing fats by slight modifications of the usual thiosulfate titration procedures. The prolongation of the induction period by some natural antioxidants and several phenolic compounds is proportional to the amount used. A t the end of the induction period the
level of peroxide in lard or lard-cod liver oil mixtures is fairly uniform, irrespective of the length of the induction period or of the original peroxide content. In the case of one natural inhibitor, W24, which was extensively studied, the effectiveness varied inversely with the amount of peroxides in the fat mixture whether these had accumulated slowly or were added in the form of an oil of high peroxide content. Under such conditions there seemed to be a mutual destruction of antioxidant and active peroxides. Some of the difficulties in obtaining reproducible data are discussed.
ATURALfats R. B. FRENCH, H. S. OLCOTT, AND H. A. MATTILL induction period of lard and of lard-cod liver oil mixtures as State University of Iowa, Iowa City, Iowa exposed t o measured by oxygen absorption. oxygen exhibit the typical characteristics of an autocatalytic oxidaThe experiments reported here were a n attempt at a critical tion: a latent or induction period of variable length during analysis of this method, with a view also to clarifying the details of the reaction. Some of the aspects which have been which the amount of oxygen absorbed is very small, followed by a period of rapidly accelerating oxygen absorption. The studied are the relation of the amount of inhibitor to the onset of rancidity usually coincides with or follows shortly after prolongation of the induction period, the effect of the peroxide the end of the induction period. level on the induction period and on added inhibitors, the influence of an inhibitor added to fats after the end of the inMany methods have been used to determine the length of duction period, and related topics. the induction period and to follow the progress of the underlying reactions. The rate and extent of t h e absorption of Methods oxygen have been determined by both manometric and gasometric apparatus. I n the latter stages of the oxidation, T o determine the length of the induction period by the extensive changes occut in acid value and iodine number. oxygen absorption method, a modification of the apparatus Variations in the amount of organic peroxides have been described by Greenbank and Holm (9,16) has been used: considered significant (16,16). Aldehyde or other products Erlenmeyer flasks (250 cc.) with lips for mercury seals and of oxidation develop color in the presence of the Kreis (12) containing the test fat are immersed in a constant-temperature and von Fellenberg (7) reagents; with limitations, such water bath and are connected by ground-in glass stoppers to Ycolor reactions are used t o detect rancidity. Issoglio (11) shaped mercury manometers (Figure 1A). Oxygen is passed in estimated the extent of oxidation by titrating t h e waterto each flask through a side arm, allowing the air in the flask to escape a t the ground-glass joint held open by a small wedge. A t soluble volatile constituents with potassium permanganate. the end of 5 minutes, the oxygen stream is discontinued, the flask The keeping qualities of fats have been measured by methylis secured firmly to the manometer, mercury is placed in the seal, ene blue fading time (10, 13). B u t the organoleptic tests, and after temperature equilibrium has been attained the stopcock in the side arm is closed. By means of a stoppered rubber tube depending upon taste and smell, are still the final criteria for and screw clamp connected t o the bottom of the manometer, the rancidity (6). level of the mercury is now adjusted to 1-2 mm. below the upper The exact significance of these and other tests is still unplatinum contact. A rise in the level of the mercury produced certain. Some of the reasons for this confusion are indicated by the absorption of approximately 1 cc. of oxygen completes a circuit through a magnet actuating a marker on a slow-moving by Barnicoat (1) who concludes that “the active oxygen and kymograph. Impulses are sent through the open circuit every Kreis values at which rancidity becomes perceptible vary 15 minutes by clock contacts. A record of the time of the begingreatly (a) for a given fat exposed to different conditions of ning of oxygen absorption is thus obtained. For a series of extemperature and light, and (b) for fats of different composiperiments in which it was necessary to make determinations at the precise end of the induction period the platinum contacts tion when subjected to identical conditions.” Coe and were connected in series with a source of current and a buzzer. LeClerc (6) have also emphasized the possible discrepancies Two samples of fat with differences in induction period of 1 hour between estimations of rancidity by peroxide determinations or less were considered to have equal stability. a n d by the organoleptic tests. I n studies reported previously (2, 16, 19, ZO),antioxidants I n order to study the rate of oxygen absorption during and were evaluated according t o their ability to lengthen the just subsequent to the induction period, the manometers were connected by rubber tubing, supplied with pinchcocks, to a 1 The first two papers in this aeries appeared in 1931 (f5)and 1934 (19).
”
724
JUNE, 1935
INDUSTRIAL AND ENGINEERING CHEMISTRY
725
liver oil was subjected to irradiation from a mercury vapor common buret and reservoir, the height of which was adjustlamp until a mixture with lard (10 drops to 5 grams) gave an able (Figure 1B). The system was then filled with water or induction period of 6 to 10 hours. (The cod liver oil was Brodie's solution (10,000 mm. = 1 atmosphere). Frequent added to the lard sample before the mixture was pipetted into measurements of pressure a t constant volume indicated the the flasks.) Irradiation of the cod liver oil decreased its precise amount and rate of oxygen absorption. During each iodine number and increased the peroxide content besides manometric run the slight changes in temperature and atmosshortening the induction period of the fat mixture. pheric pressure were memured by the pressure changes in a flask containing no fat, and the correction was applied to the Peroxide determinations have been widely used in following other determinations. A possible disadvantage of this the development of rancidity in fats. Yule and Wilson (27) method is mentioned by Milas ( I 6 ) , who points out that the have described a titrimetric method for peroxides in gasolines, rate of oxygen absorption is influenced by pressure changes. based upon the oxidation of ferrous iron by peroxides in the I n these measurements only small changes of pressure were presence of thiocyanate. An attempt was made to apply this method to the colorimetric determination of peroxides in possible. The buret measured maximum differences of 50 cm. water (4 cm. mercury). When changes of such magnifats. As modified, it gave quantitative results with hydrogen tude were approached, it was necessary to readjust the system peroxide, but when an oxidized cod liver oil was shaken with by admitting more oxygen into the reaction flasks. The the reagent, the color of ferric thiocyanate, which developed results indicated that this factor could be disregarded. immediately, gradually faded. This may be correlated with the observations of Stirling (24) on the effect of iron in perSince the fat was not stirred, only its surface was exposed to oxygen. T h a t a thin layer of fat allowed sufficient pene-• oxide oxidations. The fist action of the reactive peroxides is to oxidize the iron which then acts as an intermediary in the tration of oxygen is indicated in Figure 2 . Quantities of a further oxidation of the fat. lard-cod liver oil mixture varying from 1 to 10 grams were Since the color reaction was unsatisfactory, it was decided, placed in flasks under oxygen at 50" C. and the amount of absorption was measured. Up to a weight of 7 grams of fat after critical study, t o use the titration method based upon the quantity of oxygen absorbed was almost directly proporthe quantitative oxidation of potassium iodide to iodine b j peroxides and subsequent titration with sodium thiosulfate tional to the amount of fat. Five-gram samples of fat were therefore generally used and the data have absolute as well as Various technics have been described (4, I C ) . Wheeler (26) relative quantitative signifigives an e x t e n s i v e bibliog n cance. raphy on the subject. I The following p r o c e d u r e The characteristics of each gave consistent results : curve in Figure 2 and succeeding figures have been conDissolve a weighed s a m le firmed in a t least one more of a b o u t 1 g r a m of fat pending upon the active o x y and usually several detergen content) in 10 cc. of a mixminations. Oxygen absorpture of glacial acetic acid and. tion is given in terms of chloroform (2 to 1) and add negative w a t e r p r e s s u r e . about a gram of powdered. potassium i o d i d e . F i l l the The end of the i n d u c t i o n flask with nitrogen and hest, period corresponded with a i n a b o i l i n g water bath for. negative pressure of 7 to 10 exactly one minute with con.. cm. of water; 10 cm. indistant shaking. Remove the flask, add 50 cc. of water, and cated the absorption of 1 cc. titrate with 0.002 N sodiux. of oxygen. thiosulfate, using starch as ar.. It was necessary to pay indicator. I t a p p e a r e d un.. necessary to free the glacial particular attention to cleanacetic acid of readily oxidiz.. FIGURE 1. OXYGEN ABSORPTION APPARATUS liness of glassware in order able material (8.2). Carbon. to obtain consistent results. A . System for determining length of induction period: tetrachloride could be sub.. 1. 250-cc. flask with ground-in glass connection: the 5ask is immersed Imperceptible traces of oxistituted for chloroform with.. in a stirred, constant-temperature b a t h (not shown) 2. Li for mercury seal out change in t,he character of' dizing fat catalyze the oxida3. S i l e arm for introducing oxygen the results (4). tion. Newton (18)used only 4. Y-manometer 5. Electrical contacts for indicating pressure decrease when mercury in new flasks. In this laboraused in manometer Antioxidant Concentra-, tory, boiling the flasks with B . System for determining pressure changes i n A a t desired intervala: tion and Induction 6. Common connections for b a t t e r y of flasks hot 20 per cent a l k a l i and 7. 50-cc. buret Period washing with water before a 8. Counterpoised leveling bottle: the ,5uid (water or Brodie's solution) is shaded i n the glass parts and unshaded in the rubber tubing of the manoI n general, the prolongachromic acid treatment remetric system tion of the induction period of' moved all traces of the oxia fat by an inhibitor is apdized fat. Laug (IS) has uointed out the necessitv of uroximatelv DroDortional tc' multiple rinsings in order t o remove traces of chromic acid. the amount of inhibitor used (Fi'gure 3). Two antioxidants, W24 and P96, which were more extensively studied, were fracSmall amounts of chromic acid seemed not t o affect the induction period of lard. tions of the unsaponifiable lipids of wheat germ oil and palm oil prepared in connection with other researches, and used here Although moisture retards the oxidation of tlutter fat (8), because of the convenient increase in induction period afthe addition of small amounts of water had no noticeable forded by the addition of 1 mg. to 5 grams of the fat ( 2 , 2 0 ) . effect on the induction period of a standard lard-cod liver oil JV52 and W4113 (Figure 4) were two other concentrates from mixture or of a carefully dried lard. The accidental introwheat germ oil. duction of mercury, used as a seal, into the fat mixture was without effect upon the length of the induction period. The effect of concentration on efficiency has been studied Cod liver oil mas added to the lard to decrease the induction in less detail on a few phenolic antioxidants. With hydroperiod to a convenient length of time. A thin layer of cod quinone, a-naphthol, orcinol, thymohydroquinone, guaiacol,
be..
.
I
&
I
INDUSTRIAL AND ENGINEERING CHEMISTRY
726
VOL. 27. X O . 6
T I M E IN HOURS
FIGURE 2. TIOS
OXYGENABSORPOF A LARD-CODLIVER OIL MIXTURE
Temperature, 50' C . ; the curves represent the rate of oxygen absorption for 1, 3, 5, 7, and 10 grams of the mixture.
FIGURE3.
REL.4TION
The substrate in A and C was lard-cod liver oil mixture, in B and D , lard alone; the antioxidant in A and B was W24, in C and D . P96.
Peroxide Concentration During the induction period of lard or lard-cod liver oil mixtures] the rates of oxygen absorption and peroxide production are slow but measurable. The end of the induction period is characterized by a sudden increase in the rate of both reactions. If the time of transition from a slow to a rapid rate of oxygen absorption is conditioned by the attainment of a certain definite concentration of active peroxides, it should be possible t o determine this fact by analyses of numerous TABLE I. EFFECTIVEKESS OF
RELATION TO
A4NTIOXIDANTS IIi CONCEIiTRATIONa
Amount, Mg.
Hydroquinone
0
0.1 0.2 0.3 n 5
Induction Period,
Hr.
Substance
Amount, Mg.
14 37
Thymohydroquinone 0 0.5
55 215
1.0 2.0
an
TE\I-
AND
and resorcinol, protection is also fairly proportional to the amount added (Table I).
Substance
OF
CONCENTRATIOX OF ANTIOXIDANT TO LENGTHOF I N DUCTION PERIOD PERATURE
The substrate "as 5 grams of lard, temperature, 75' C . each compound represent a typical single run.
Induction Period, Hr. 14 17 24
The results on
samples of different induction periods at the exact end (as closely as can be determined) of the induction period. Table I1 presents the results of several determinations. While there is no constant value for peroxides a t the end of the induction period, all the results lie within a fairly narrow range. Immediately thereafter the peroxides increase a t a more rapid rate; some of the variability in the results of Table I1 may be due to the difficulty of determining the exact end of the induction period. These data indicate that the antioxidants delay not only the rapid uptake of oxygen but also the accumulation of peroxides. By the time the peroxide level has attained the height indicative of the end of the induction period, the antioxidant has entirely disappeared; none of its activity can be recovered in the unsaponifiable portion of the oxidized fat. When the amount of irradiated cod liver oil in the mixture
FIGURE 4. INFLUENCE OF LEVELOF ACCELERATOR o s IXDUCTION PERIOD OF L.4RD AND ON EFFECTIVENESS OF ADDED ANTIOXIDAXTS
mas increased (eatablishing a higher le\ el of peroxide-), there was a corresponding decrease in the length of the induction period as well as a decrease in the effectiveness of added antioxidants (Figure 4). This decreased effectivenessof antioxidants in fats of higher peroxide content could also be demonstrated when the peroxides were allowed to accumulate in the natural course of autoxidation. Figures 5 and 6 illustrate the effect of an inhibitor added a t different times during and after the induction period upon the rates of oxygen absorption and of peroxide formation. As the concentration of peroxidea increased, the protection afforded by the antioxidant diminished. The oxidation of the fat could proceed so far that the antioxidant in the initial concentration used was almost totally ineffective, but if enough was added its protective action could -till be demonstrated. The antioxidant stopped not only the uptake of oxygen in the rapidly oxidizing mixture but also the formation of peroxides. Oxygen absorption may .till have been taking place at a greatly lowered rate, not detectable because the absorption was masked by the production of gaseous products in the interaction of the antioxidant and peroxides. The data of Figure 6 were obtained as follows: Two 1liter Erlenmeyer flasks containing a thin layer of the fat mixture were filled with oxygen, stoppered, and placed in a con5tant-temperature oven. Samples were withdrawn for analysis, and the antioxidant was added a t the times indicated. In order t o compare with other data, the antioxidant was added in quantities such that the recorded figure represents the amount present in each 5 grams of fat. Each point repre-ents an average of duplicate determinations. A slight increase in pressure in the system is evident in several instances in the data of Figure 5 . It was produced following the addition of an antioxidant to a rapidly oxidizing fat mixture; a corresponding drop in peroxide content was also observed (Figure 6). Apparently the decrease in efficiency of added antixodant as autoxidation proceeds is due to mutual destruction of peroxides and antioxidant; evidence for this is the reduced concentration of peroxide, the evolution of gas, and the fact that no material possessing antioxygenic activity can be extracted from the fat mixture after the end of the induction period. Under such conditions the effect of the antioxidant seems t o reside in its ability to destroy active peroxides. The latent period between the time of introduction of antioxidant and the drop in peroxide level (Figure 6) suggests an appreciable time interval for this reaction. The limitations of the absorption apparatus prevented the demonstration of a correlating lag in gas evolution. Since a large proportion of the peroxide is not destroyed, even though
JUNE, 1935
INDUSTRIAL AND ENGINEERING CHEhlISTRY
oxygen absorption temporarily ceases, the portulation of a t least two differe n t k i n d s of peroxides (active and inactive) (3, 16, 25) has much support. A temporary posit i r e prc.ssure w a s also observed when 3 2 24 3L 48 TIME IN HOURS the oxygen absorpFIGURE 3. EFFECTOF ADDITIONOF tion of !ard contain.\NTIOXIDANT UPON OXYGEN ABSORPing varj ing amount3 TION AT DIFFERENTSTAGESOF FAT of cod liver oil was OXIDATION folloir-eclby means of Substrate, lard-cod liver oil mixture; temperature, 50' C . ; antioxidant, W24. Solid the water inanomedots represent determinations on duplicate ters (Figure 7). samples which were started 12 hours before those indicated b y circles. The positive p r e s (5, Substrate fat alone. fp) , T h r e e samples t o which 1 mg. of s u r e as m o s t antioxidant was added a t t h e start, and then marked with the each treated as indicated b y captions a n d diverging curves. mixture containing ( c ) Three milligrams of antioxidant added a t start. the least cod liver oil. I n t h e o t h e r c a s e s it was probably masked by the more rapid absorption of oxygen. The increase in pressure was due neither to the release of dissolved gases nor to t h e production of carbon dioxide since I2 24 3 k 4 it Tvas observed both TIME IN HOURS after exposure of the FIGURE 6. EFFECT OF AUDITION OF fat to a high vacuum ANTIOXID.4NT UPON PEROXIDE CONand in the presence ST.4GES CENTRATION AT DIFFERENT OF OXIDATION OF FAT of a carbon dioxide (a1 Substrate f a t alone. absorbent. T h e ( b ) , ( c ) Samples t o a h i c h 1 nig. of antin a t u r e of the gas osidant was added a t t h e s t a r t , and then each, treated as shown b y captipns a n d dievolved is unproved, verging curves. T h e higher initial peroxide content (b'i of these two samples is due t o but the assumption t h e use of R different lot of lard a n d cod that, a t least in part, liver oil. ( d ) T h e branching of t h e curve, shows it is oxygen from the t h e agreement t o be expected in different runs. decomposition of the peroxides seems tenable. Using p u r i f i e d oxygen, an attempt was iiiade to identify a n y ofher gases l i b e r a l e d here as well as in those experinieiits in which an antioxidant was 2 k 6 added t o a rapidly T VFI'l"OJ?S oxidizing fat. The FIGURL7 . COL-RSE OF OXYGEN only extraneous gas -ZBSORPTIOS OF DIFFEREUT L~ R D CODLIVEROIL JIIXTVRES that coiild be found was hydrogen (by Temperature, 50' C . ; t h e curves represent the absorption of oxygen by &gram explosion pipet), in samples of lard t o which have been added 2 , 4, 6, 8 , and 10 drops of cod liver oil as amounts up to 1 cc. indicated. in the cas mixture withiiran-n from fla-ks containing 5 grams of fat. Carotene as a Prooxidant Carotene not only decreased the length of the induction peririd ('2, 1.9, 21) but 31'0 increased the rate of oxygen absorption (luring the period ( i f active oxidation.
----e
i27
TABLE11. RELATION OF PEROXIDES T O LSSGTH O F INDUCTION PERIOD -Induction Temperature. Substrate Lard
O
C.
90
blg Anti-
oxidant
4 5
Length, hr 4.5 4.5 17 3 19.6 23.3 5.3 6.8 18.0 17.5 2.1 2 1 .5 :i 5.5 17 (I 21 3
1 0 10 0 9 2
146,O 6.0 22.0 20 0
w24 0 0 3 4 5 0 1
,
3 0 0 1
1
50
I
-
PeriodPeroxides-Start, mg. End, mg. 0 Y IO3 0 X 10: per I. f a t per g. fat 1.5 26 23 14 28 23 8 20 48 35 42 16 14 17 34
5 9 6.0
22 30
37 35
57 43
40 3s
Discussion of Results
These relations between peroxides, inhibitors, and the induction period of fats offer a striking parallelism to the observations on gasolines made by Egloff and his co-workers (17'). They found, furthermore, that some gasolines were refractory to protection by antioxidants, and the present writers have obtained limited evidence that lards may also vary somewhat in their response to inhibitors, irrespective of the leiigt'hs of their induction periods. Such variations make it difficult t'o obtain reproducible results. Another difficulty is the variable relation between the peroxide level and the induction period of different lard-cod liver oil mixtures. Thus, a lard-cod liver oil mixture having an induction period of 6 hours (at 50" C.) and a peroxide level equivalent to 0.030 mg. of 0 per gram had been used over a period of months. Another lot of cod liver oil was irradiated unt,il the peroxide level of a mixture with a fresh lard was again equivalent to 0.030mg. of 0 per gram. This mixture had an induction period of only 2 hours (at 50" C.), although the peroxide content was the same as that of the previous sample. The difference might be explained by postulating different quantities of antioxygenic material in the oil and fat samples, or, less likely, different amounts of other accelerators. Attempts to transfer the significance of results obtained 011 one type of fat to another disclose further difficulties. For example, some of the data of Coe and LeClerc (6) show t'liat under certain conditions the peroxide curve exhibited no break when corn oil and cottonseed oil became rancid; the rate of formation of peroxides n-as equally as rapid before as after the onset of rancidit,y. Some types of fats likewise exhibit no marked alteration in rate of oxygen absorption with the approach of rancidity. Results of this nature obviously suggest that fundamental data must be obtained on purified fatty acids and esters rather than on natural fats of complex make-up. Research along these lines is in progress.
Literature Cited (1) B a r n i c o a t , C . R., J . SOC.C h e m Ind., 50,361T (l'X31). (2) B r a d n a y , E. M . , and Mattill, H . A,, J . -477~. Cirena. Soc.. 56,2405 (1934). (3) B r a n c h , G. E. K., Ilmquist, H. J., a n d Goldsa.orthy, Ibid., 55,4052 (1933).
E. C.,
728
INDUSTRIAL AND ENGINEERING CHEMISTRY
(4) Briggs, L. H., J . Dairy Sci., 3,61, 70 (1931). ( 5 ) Coe, M. R., and LeClerc, J. A., IND. ESG. CHEM.,26,245 (1934). (6) Davidsohn, J., Chem.-Ztg., 54, 606 (1930). (7) Fellenberg, T. von, M i t t . Lebensm. Hug., 15, 198 (1924). (8) Greenbank, G.R., and Holm, G. E., IND.ENG.C H m f . , 16, 598 (1924). (9) Ibid., 17, 625 (1926). (10) Ibid., Anal. Ed., 2, 9 (1930). (11) Issoglio, G., Snn. chim. applicata, 6,1 (1916); Kerr, R. H., and Sorber, D . G., IKD.ENC.CHEV.,15, 383 (1923). (12) Kreis, H., Chem.-Ztg., 26, 1014 (1902). EXG.CHExf., Anal. E d . , 6, 111 (1934). (13) Laug, E. P., IND. (14) Lea, C. H., Dept. Sci. Ind. Research (Brit.), Rept. Food Inaestigation Board, 1929, 30 (1930). (15) Mattill, H. A,, J. Bid. Chem., 90, 141 (1931). (16) Milas, N. A . , J . A m . Chem. Soc., 52, 739 (1930); Chem. Rez., 10, 295 (1932).
VOL. 27, NO. 6
(17) Morrell, J. C., Dryer, C. G., Lowry, C. D., Jr., and Egloff, G., I N D . ENQ.CHEM., 26,497 (1934). (18) Newton, R. C., J . Oil Soap, 9,247 (1932). 56,2492 (1934). (19) Olcott, H. S., J . Am. Chem. SOC., (20) Olcott, H. S., and Mattill, H. A , , J . B i d . Chem.. 93, 59, 65 (1931). (21) Olcovich, H. S., and Mattill, H. A . , Ibid., 91, 105 (1931). (22) Orton, K. J. P., and Bradfield, h. E., J . Chem. Soc., 125, 960 (1924). (23) Royce, H. D., IND. ESG.CHEM.,Anal. Ed., 5, 244 ~ 1 9 % ) . (24) Stirling, 3. D., Biochem. J., 28, 1048 (1934). (25) Taffel, A., and Revis, C., J . SOC.Chem. Ind., 50, 8 i T (1931). (26) Wheeler, D. H . , J . Oil Soap, 9, 89 (1932). (27) Pule, J. A. C., and M'ilson, C. P., Jr., I N D .ENG.CHEI., 23, 1254 (1931). RECEIVED December 2 6 , 1934.
Rate of Absorption of Carbon Dioxide Effect of Concentration and Viscosity
of Normal Carbonate Solutions The initial (steady state) rate of absorption of pure carbon dioxide a t a pressure of one atmosphere is measured for solutions of sodium carbonate up to 4 normal and of potassium carbonate up to 7 normal a t 30' C. An equation of the form,
LAUREN B. HlTCHCOCK . O D HENRY 31. CADOT University of Virginia, Charlottesville, Va.
T
satisfactorily reproduces the experimental results over the entire range, where dV/AdO represents initial current density, ci and cs are interfacial and main-body concentrations, respectively, of the reactants, and z is viscosity. The constants k and b are determined by the experimental data and are approximately 10 per cent higher for the potassium compound. The measurements were made under identical conditions with those employed in determining absorption rates for the analogous hydroxides, permitting for the first time a quantitative comparison of the absorption rates of the two carbonates and the two hydroxides as a continuous function of concentration. The initial (steady state) rate of absorption by pure water is also reported. Apparently discordant results of earlier investigators may be satisfactorily interpreted in the light of the new evidence.
HE initial rate of absorption of pure carbon dioxide gas by stirred solutions of potassium hydroxide and sodium hydroxide a t 30" C. was studied by Hitchcock (5) as a function of caustic concentration and liquid viscosity. It was found that t h e results could be readily interpreted by means of a diffusional mechanism in which the rate of absorption was directly proportional to the concentrations of the reactants and inversely proportional to a function of the viscosity. I n view of the general industrial use of soda ash solutions as absorbents, it seemed desirable to make a similar study of the behavior of aqueous solutions of sodium and potassium carbonates and compare the rates of absorption into these less reactive media with those obtained for the respective hydroxides under identical absorption conditions. Consideration of the literature furnished a n additional incentive to undert,aking this investigation, for i n >pitc of the large number of experiments bearing directly on t'he subject, the results of different investigators appear to be exceptionally discordant. While it is true that the several conclusions are supported by experiments of a qualitative character for the most part, the disagreement cannot be explained satisfactorily on the basis of experimental error alone. The chief difficulty seemed t o be that no two investigators used the same solute concentrations in the same type of absorption equipment, and no one investigator varied solute concentration over a sufficient range. Ledig and Weaver ( 7 ) found that a bubble of pure carbon dioxide gas rising through a dilute solution of sodium hydroxide at 25" C. was absorbed many times faster than if i t rose through sodium carbonate solution of the same concentration, while Davis and Crandall ( 2 ) reported that pure carbon dioxide gas was absorbed through a horizontal liquid surface by stirred 0.1 molal sodium carbonate at the same temperature slightly more rapidly than by 0.1 molal
